EF-Tu receptor

EFR, like other proteins, undergoes translation in a cell's ribosomes. After the primary structure of the protein has been formed it must fold into its three dimensional tertiary structure to become functional. This occurs in the endoplasmic reticulum (ER). While in the ER, this primary polypeptide chain undergoes a regulatory process known as ER-quality control (ER-QC) to help ensure it folds into the correct 3-D structure. and avoids. ER-QC process consists of a series of chaperone proteins that help guide the folding of the EFR polypeptide chains, preventing the aggregation of many polypeptide chains into one large group. Proteins that have not folded are kept in the ER until they have folded into their correct 3-D shape. If folding does not occur then the unfolded protein is eventually destroyed.[9][10]

One of the control mechanisms of EFR is the protein Arabidopsis stromal-derived factor-2 (SDF2). A genetic variant of the A. thaliana plant that did not have the gene to encode for this protein had a far lower production of functional EFR proteins. SDF2 also cannot be substituted for other enzymes in EFR production. Experimental analysis indicated that EFR is destroyed in the cell when it is produced without SDF2, though the mechanism of this action is unknown. Other proteins that are required for the proper synthesis of EFR include Arabidopsis CRT3 and UGGT, which are members of the EFR-QC and act as chaperones to help folding.[10]

EFR receptors have a high affinity for the EF-Tu PAMP. This has been proven analytically through competitive binding assays and SDS-PAGE analysis. When EFR binds to EF-Tu, the basal resistance is activated.[2] This response happens after an infection has already been established and it is important to the plant immune system because it prevents the spread of the pathogen throughout the plant.[11] Only bacteria that have a high amount of EF-Tu are effectively inhibited by EFR, such as Agrobacterium tumefaciens.[2]

Like EFR, FLS2 (flagellin-sensing 2) is a plant receptor-like kinase that acts as a PRR in the plant innate immune system.[10][12] Instead of binding to EF-Tu, it binds to flagellin, another highly conserved structure present on many pathogens. It, like EF-Tu, is a good target for the plant immune system since it is so widespread. It also triggers an immune response in a larger variety of plants than EF-Tu.[2] The immune response triggered by FLS2 is very similar to the one that is triggered by EFR and the enzymes that are activated by both receptors likely come from a common pool that is found in many cells. This indicates that the two receptor pathways converge, which has been shown to occur at the ion channels in the plasma membrane.[10][13] By perceiving multiple PAMPs, a plant is able to respond to a pathogenic infection more quickly and efficiently, as well as respond to a wider array of pathogens.[10]